HYDRAULIC CONTROL ARRANGEMENT 4J6058 - Caterpillar

Operation
When the 3T9343 Switch Group is held in your hand, the contacts are OPEN. But, when installed in the filter housing, the bypass spool will push the pin to the left and close the contacts. See illustration. This keeps the EMS from sounding the alarm. At this time, the filter bypass spool is in the normal position (nonbypass).
Construction and operation of the oil filter bypass switch.A temperature switch, such as the 9G3341 Switch Assembly, is always used in parallel with 3T9343. The temperature switch is closed when the oil temperature is below 43°C (110°F), and inhibits any effect of cold oil on the bypass switch. Cold oil often bypasses a filter and this is a good reason to warm up the machine before putting it to work. The reason for the temperature switch is to keep the EMS alarm from sounding, even if the filter bypasses and opens the bypass switch while the machine warms up. When the oil temperature reaches 52°C (125°F), the temperature switch opens and permits the bypass switch to correctly indicate a true filter bypass condition if it occurs.
When conditions cause the filter bypass spool to just begin to MOVE, the bypass switch opens and causes a level 3 warning (alarm sounds). However, the filter is not yet actually bypassing oil because the spool is only beginning to move into bypass position to allow oil to flow around the filter. Actual oil bypassing occurs ONLY after the pressure drop across the filter increases enough to place the spool in the true bypass position. EMS can not tell precisely when actual bypassing takes place.
The actual point of bypassing is not important. The design of the bypass spool and spring causes a warning when the filter needs to be replaced to protect the power train. Remember, if the system functions correctly, a plugged filter can not be indicated until the oil temperature reaches 52°C (125°F).
Complaints And Solutions
The following are common reasons for complaints regarding EMS power train warnings.
EMS Warning Comes On With Cold Oil; Warning Stops When Oil Becomes Warm
Check the temperature switch to see if it is open (faulty) below 43°C (110°F). Check for an open wire between this switch and the bypass switch.
EMS Never Gives Warning To Change Filter
... The bypass or temperature switch can be shorted (never opens).
... Wiring between these switches and EMS panel can be shorted to ground (chassis).
... EMS panel can be defective.
EMS Gives Warning Only After Power Train Oil Is Warm
The EMS is functioning correctly and this is not a false alarm. Look for the following.
New Machines With Less Than 200 Hours
1. When the machine is first started at the factory, a special small micron filter is installed to remove particles smaller than those removed by the larger micron standard filter. If the small micron filter was not replaced with the standard filter before the machine was shipped, bypassing may occur too soon. Simply install a new Cat filter and return the machine to work.2. The hydraulic system might